Re: [PATCH] adfs: add hexadecimal filetype suffix option

[Arnd Bergmann <arnd@arndb.de>]

On Friday 21 January 2011 18:26:58 Russell King wrote:
> On Fri, Jan 21, 2011 at 05:47:17PM +0100, Arnd Bergmann wrote:
>
> > Would you be able to take a look at this? The straightforward approach
> > would be to add a mutex to adfs_sb_info and use that in place of
> > lock_kernel. It's mostly a matter of testing to make sure that no
> > deadlocks get introduced in the process.
> 
> Note that write support is very limited.  From memory, the only writing it
> supports is changing directory entries and writing data into existing files
> (but not extending or truncating them.)
> 
> The only thing that's supported is updating of existing directory entries,
> for which it has a read/write lock to protect against multiple callers.
> I think I assumed at the time that I wouldn't rely on the BKL, so it
> should be safe to kill it.

Makes sense. Proving that the BKL is not needed is obviously preferred
over replacing it with a mutex. After your explanation and another look
at the code, I agree that we can simply remove all references to the BKL
from adfs, unless someone can find a reason we still need it.

Stuart, could you add this patch to your series then, and give it some
testing?

	Arnd

8<-----
Subject: adfs: remove the big kernel lock

According to Russell King, adfs was written to not require the big
kernel lock, and all inode updates are done under adfs_dir_lock.

All other metadata in adfs is read-only and does not require locking.
The use of the BKL is the result of various pushdowns from the VFS
operations.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Stuart Swales <stuart.swales.croftnuisk@gmail.com>
---

 fs/adfs/dir.c   |    6 ------
 fs/adfs/inode.c |    6 ------
 fs/adfs/super.c |   13 +------------
 3 files changed, 1 insertions(+), 24 deletions(-)

diff --git a/fs/adfs/dir.c b/fs/adfs/dir.c
index 3b4a764..3d83075 100644
--- a/fs/adfs/dir.c
+++ b/fs/adfs/dir.c
@@ -9,7 +9,6 @@
  *
  *  Common directory handling for ADFS
  */
-#include <linux/smp_lock.h>
 #include "adfs.h"
 
 /*
@@ -27,8 +26,6 @@ adfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 	struct adfs_dir dir;
 	int ret = 0;
 
-	lock_kernel();	
-
 	if (filp->f_pos >> 32)
 		goto out;
 
@@ -70,7 +67,6 @@ free_out:
 	ops->free(&dir);
 
 out:
-	unlock_kernel();
 	return ret;
 }
 
@@ -276,7 +272,6 @@ adfs_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
 	struct object_info obj;
 	int error;
 
-	lock_kernel();
 	error = adfs_dir_lookup_byname(dir, &dentry->d_name, &obj);
 	if (error == 0) {
 		error = -EACCES;
@@ -288,7 +283,6 @@ adfs_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
 		if (inode)
 			error = 0;
 	}
-	unlock_kernel();
 	d_add(dentry, inode);
 	return ERR_PTR(error);
 }
diff --git a/fs/adfs/inode.c b/fs/adfs/inode.c
index 65794b8..09fe401 100644
--- a/fs/adfs/inode.c
+++ b/fs/adfs/inode.c
@@ -7,7 +7,6 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
-#include <linux/smp_lock.h>
 #include <linux/buffer_head.h>
 #include <linux/writeback.h>
 #include "adfs.h"
@@ -316,8 +315,6 @@ adfs_notify_change(struct dentry *dentry, struct iattr *attr)
 	unsigned int ia_valid = attr->ia_valid;
 	int error;
 	
-	lock_kernel();
-
 	error = inode_change_ok(inode, attr);
 
 	/*
@@ -359,7 +356,6 @@ adfs_notify_change(struct dentry *dentry, struct iattr *attr)
 	if (ia_valid & (ATTR_SIZE | ATTR_MTIME | ATTR_MODE))
 		mark_inode_dirty(inode);
 out:
-	unlock_kernel();
 	return error;
 }
 
@@ -374,7 +370,6 @@ int adfs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	struct object_info obj;
 	int ret;
 
-	lock_kernel();
 	obj.file_id	= inode->i_ino;
 	obj.name_len	= 0;
 	obj.parent_id	= ADFS_I(inode)->parent_id;
@@ -384,6 +379,5 @@ int adfs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	obj.size	= inode->i_size;
 
 	ret = adfs_dir_update(sb, &obj, wbc->sync_mode == WB_SYNC_ALL);
-	unlock_kernel();
 	return ret;
 }
diff --git a/fs/adfs/super.c b/fs/adfs/super.c
index 2d79540..06d7388 100644
--- a/fs/adfs/super.c
+++ b/fs/adfs/super.c
@@ -14,7 +14,6 @@
 #include <linux/mount.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
-#include <linux/smp_lock.h>
 #include <linux/statfs.h>
 #include "adfs.h"
 #include "dir_f.h"
@@ -120,15 +119,11 @@ static void adfs_put_super(struct super_block *sb)
 	int i;
 	struct adfs_sb_info *asb = ADFS_SB(sb);
 
-	lock_kernel();
-
 	for (i = 0; i < asb->s_map_size; i++)
 		brelse(asb->s_map[i].dm_bh);
 	kfree(asb->s_map);
 	kfree(asb);
 	sb->s_fs_info = NULL;
-
-	unlock_kernel();
 }
 
 static int adfs_show_options(struct seq_file *seq, struct vfsmount *mnt)
@@ -359,15 +354,11 @@ static int adfs_fill_super(struct super_block *sb, void *data, int silent)
 	struct adfs_sb_info *asb;
 	struct inode *root;
 
-	lock_kernel();
-
 	sb->s_flags |= MS_NODIRATIME;
 
 	asb = kzalloc(sizeof(*asb), GFP_KERNEL);
-	if (!asb) {
-		unlock_kernel();
+	if (!asb)
 		return -ENOMEM;
-	}
 	sb->s_fs_info = asb;
 
 	/* set default options */
@@ -485,7 +476,6 @@ static int adfs_fill_super(struct super_block *sb, void *data, int silent)
 		adfs_error(sb, "get root inode failed\n");
 		goto error;
 	}
-	unlock_kernel();
 	return 0;
 
 error_free_bh:
@@ -493,7 +483,6 @@ error_free_bh:
 error:
 	sb->s_fs_info = NULL;
 	kfree(asb);
-	unlock_kernel();
 	return -EINVAL;
 }